Nano-sized γ-Al2O3 Research Articles

Characteristics of alumina particles in dispersion-strengthened copper alloys

Two types of alumina dispersion-strengthened copper (ADSC) alloys were fabricated by a novel in-situ reactive synthesis (IRS) and a traditional internal oxidation (IO) process. The features of alumina dispersoids in these ADSC alloys were investigated by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. It is found that nano-sized γ-Al2O3 particles of approximately 10 nm in diameter are homogeneously distributed in the IRS-ADSC composites. Meanwhile, larger-sized, mixed crystal structure alumina with rod-shaped morphology is embedded in the IO-ADSC alloy. The IRS-ADSC composites can obtain better mechanical and physical properties than the IO-ADSC composites; the tensile strength of the IRS-ADSC alloy can reach 570 MPa at room temperature, its electrical conductivity is 85% IACS, and the Rockwell hardness can reach 86 HRB.

Investigation of different precipitating agents effects on performance of γ-Al2O3 nanocatalysts for methanol dehydration to dimethyl ether

This research includes synthesis of nano-sized γ-Al2O3 catalyst for methanol dehydration reaction to produce DME. A co-precipitation method with four precipitants including sodium carbonate, sodium bicarbonate, ammonium carbonate and ammonium bicarbonate was used for this purpose. The catalysts were characterized by XRD, FTIR, NH3-TPD, SEM, TEM and N2 adsorption–desorption techniques. In order to investigate the catalyst activity, they were used in the fixed bed micro reactor for methanol dehydration reaction at different operating conditions. Also, a commercial γ-Al2O3 nanocatalyst was utilized for comparison purposes. The catalyst prepared by ammonium carbonate showed the highest yield of DME in comparison with other ones.

Microstructure and properties of Al2O3 dispersion-strengthened copper fabricated by reactive synthesis process

Al2O3 dispersion-strengthened copper alloy was prepared by reactive synthesis and spark plasma sintering (SPS) process. Studies show that nano-sized γ-Al2O3 particles with 27.4 nm mean size and 50-nm interval are homogeneously distributed in copper matrix. The density of SPS alloy is about 99 %, meanwhile, the electrical conductivity of sintered alloy is 72 % IACS and the Rockwell hardness can reach to HRB 91.

New Method for Synthesis Nano Size γ-Al2O3 Catalyst for Dehydration of Methanol to Dimethyl Ether

New Method for Synthesis Nano Size γ-Al2O3 Catalyst for Dehydration of Methanol to Dimethyl Ether

Influence of autogenous seeding on densification and microstructure in processing of γ-alumina nanopowders

The effect of α-Al2O3 seeds and MgO on the densification behavior and microstructure of the nanocrystalline γ-Al2O3 powder was investigated. The required α-Al2O3 seeds were produced by ‘autogenous seeding’ where the seeds were obtained by calcination of the initial nanosized γ-Al2O3 powders above its transformation temperature and incorporated into γ-Al2O3 matrix. The seeds were characterized by means of laser particle size analyzer, X-ray diffraction, and Brunauer–Emmett–Teller surface analyzer. The simultaneous influence of α-Al2O3 seeds and MgO on γ-Al2O3 behavior was evaluated by differential thermal analysis, densitometry, and electron microscopy. The results showed that simultaneous presence of MgO and seeds in γ-Al2O3 matrix has a great impact on densification and microstructural evolution. The main role of MgO and the seeds are densification enhancement and grain refinement, respectively. The grain morphology is more equiaxed and desirably finer by using smaller seeds prepared using shorter calcination times.

Optical Properties and Dependence of Optical Transmittance on the Particle Sizes of Nano-Structured Translucent .GAMMA.-Al2O3 Ceramics.

Nano-size γ-Al2O3 particles of four different sizes were synthesized by MOCVD (Metal Organic Chemical Vapor Deposition) method and then translucent nano-structured γ-Al2O3 ceramics are pelletized under a pressure of 2.5 GPa by a uniaxial compaction-method. Although these nano-structured γ-Al2O3 ceramics showed low density, they were fairly translucent. The relationship between transmittance and thickness of these specimens can be described by Lambert-Beer's law. The nano-structured γ-Al2O3 ceramics with different particle diameter and thickness have been prepared in order to clarify the dependence of particle size on the optical transmittance. The optical transmittance decreased with increasing initial particle diameter. In the case of 0.20mm thickness samples, the γ-Al2O3 with 5.6nm initial particle diameter showed an optical transmittance of about 60%. However, the optical transmittance decreases less than 5% when initial particle diameter is increased to 34.4nm. This phenomenon could be explained by Rayleigh scattering, which is the scattering due to the particle diameter being much smaller than the wavelength of light. In these visible regions (500-800nm), a scattering coefficient related with Rayleigh scattering was inversely related to the fourth power of the wavelength and directly proportional to the square of the grain size.

Nanosize Al2O3 Powder Production by Pulsed Wire Discharge

Nanosize Al2O3 powder was produced by pulsed wire discharge. The discharge was carried out at a peak current of ∼10 kA, the pulse length of ∼20 µs, and pulse energy of ∼80 J. Nanosize γ-Al2O3 powders have been synthesized by pulsed discharge of metal wires in oxygen as an ambient gas. The powder size and its distribution were controlled by the oxygen pressure.